Permittivity is a parameter of a material responding to the electric field. The material can generate induced charges under the action of external electric field, but resulting in weakening the electric field. The ratio of the external electric field of original vacuum to the electric field of the final material is called permittivity. Any kind of material has its specific permittivity value or permittivity curve in the natural world. When the material with high permittivity is placed in the electric field, the strength of the electric field will produce a considerable decrease in dielectric material. The material with high permittivity, such as dielectric insulator, is often used to produce capacitors. The electromagnetic wave has a very short wavelength in dielectric material with high permittivity, which can greatly reduce the size of the radio frequency and microwave devices.
With the rapid development of science and technology, people constantly set higher and higher standards for material application. In some cases, the needed permittivity value of the material is much greater than that of the existing material in the nature world. The existing dielectric with high permittivity can not meet the standards, which will become the bottleneck in the development of technology and related product research. Thus, artificial metamaterials are applied to achieve these purposes and solve these problems.
Metamaterial is new artificial composite structure material with extraordinary physical characteristic which does not exist in the natural materials. By placing the microstructures in ordered arrangement, the relative permittivity and the permeability of each point are changed in space. The metamaterial has the permittivity and the permeability that the common materials do not exist within a certain range to effectively control the propagation characteristics of electromagnetic waves.
The metamaterial includes a substrate and a plurality of artificial microstructures attached to the substrate. The artificial microstructures are composed of metal wires and have a certain geometrical shape formed by the metal wires. The artificial microstructures are placed on the substrate in an array arrangement. The substrate is a structure that serves to support the arranged artificial microstructures. The substrate can be made of any materials different from that of the artificial microstructures. The two different types of materials of the substrate and the artificial microstructures are overlapped together to produce an equivalent permittivity and permeability in space, and the two physical parameters respectively correspond to the electric field response and magnetic field response of the entire material. The electromagnetic response of the metamaterial is dependent on the characteristics of the artificial microstructures, and the electromagnetic responses of the artificial microstructures are mostly dependent on the topological characteristics of the metal wires and the size of metamaterial units. The size of each metamaterial unit is depended on the needed electromagnetic waves responded by the artificial microstructures. The size of each artificial microstructure is usually about one tenth of the wavelength of the electromagnetic waves that need to respond, otherwise the arrangement formed by the artificial microstructures cannot be considered to be continuous.
Referring to FIG. 1, in the typical production process of metamaterial, “I” shaped artificial microstructures are usually applied to change the distribution of the permittivity in space. The metamaterial can be formed by the array arrangement of substrate units attached by artificial microstructures. The size range of each substrate unit is from one tenth to one fifth of the wavelength of the electromagnetic waves. In a limited space, the change range of the size of the “I” shaped artificial microstructure is limited, and accordingly the changeable range of the permittivity of the metamaterial unit is limited too.